As is known, lift trucks are often used to lift and carry loads, such as rolled carpets. Lift trucks usually include: (a) steerable and drive wheels for propelling and maneuvering the lift truck over a surface, (b) an upright and carriage system for handling loads and (c) a power source and drive system for propelling the truck and operating truck systems including the upright and carriage system. Typically the uprights include multiple stages in order to allow the load to be lifted to a required height above ground level including, for example, up to twenty-eight feet above ground level. This allows loads to be positioned on storage racks, into over-the-road trailers, into ocean-going freight containers or the like.
The present invention relates to a five stage upright for a lift truck. Two different types of five stage uprights are known in the art. The first, known as a “six pack”, incorporates two “triple stage” uprights that are fastened one in front of another. This arrangement uses a total of six rail sets or mast sections arranged generally as illustrated in FIG. 10a. The hydraulic systems for these uprights are designed for the normal six thousand to eight thousand pound loads of the truck models to which the six-pack upright is normally attached. The other method is known as “quad-plus-one”. In a quad-plus-one upright a conventional four rail or “quad” upright has an additional rail set or mast section added in front of the existing four mast sections as illustrated in FIG. 10b. 
The prior art six-pack and quad-plus-one uprights are effective to provide five stages to reach a given lift height. It should be appreciated, however, that each of these designs suffers from a number of significant draw-backs. In the case of the six-pack upright, six separate mast sections are utilized in order to provide a five stage lift. The extra mast section adds unnecessary weight to the upright which reduces load capacity and adversely affects the battery life of an electrically powered lift truck. The stacking of the mast sections in the fore/aft direction also increases the load center which further reduces lifting capacity. It also adds length to the truck thereby increasing the aisle space necessary to allow effective operation of the truck.
The quad-plus-one upright suffers from similar disadvantages. Once again, the fore/aft stacking of the mast sections increases the load center thereby reducing lifting capacity. It also increases the overall length of the truck thereby limiting operation of the truck to warehouses and areas with wider aisle ways. Since space within a warehouse is limited, wider aisle ways reduce available storage space which is a primary customer concern.
The present invention relates to a five stage upright specially designed to provide the desired relatively high lift height with a relatively low overall truck height that allows placing loads on racks up to twenty-eight feet in height as well as into over the road trailers and ocean going freight containers. The five stage upright rail configuration of the present invention has been widened to closely fit between the drive tires of the lift truck. The widening of the rail system adds to the lateral stability of the lift truck when under load.
The “rail nest” consists of five rails arranged with the innermost three rails with the same general arrangement as a three rail nested upright where the rails are staggered forward. The additional two rails in the five-stage located outboard of the inner three rails are staggered in reverse. The result in that the depth or fore and aft dimension of the five stage rails is essentially the same as a three rail upright. This reduction in the dimension from the load face to the centerline of the drive wheels adds significantly to the load capacity of the lift truck.
There are some additional noteworthy advantages from the new arrangement. The most dramatic is the reduction of the load center: that is, the dimension from the centerline of the drive wheels to the load face. This represents a change from approximately 36 inches for the six-pack upright system and approximately 30 inches for the quad-plus-one upright system to 21.4 inches for the five stage upright of the current invention. This reduction in load center allows using a smaller upright system and a smaller base lift truck chassis to carry the same load. The nominal forklift chassis can be reduced from 8000 lb capacity with a service weight of 13,649 lb to a smaller 6500 lb capacity with a weight of 11,828 lb. The smaller chassis size reduces the initial cost as well as reducing the operating cost and energy consumption while doing the same work.
The space between the innermost rails is larger than with conventional designed five and six rail “narrow” uprights. This significantly improves the width of the “vision window” that the operator must look through. The width is similar to the spaces found in a conventional three rail upright. This also leaves room to use twin lift cylinders to lift the load engaging structure, the “carriage” and remove the normal single cylinder mounted in the center. Removing the center cylinder allows the carriage to extend backward between the front pair of rails, contributing to the reduction in load center. This is especially significant because it allows the operator to “sight down” the carpet pole to align the pole with the carpet to be handled.